xiv INTRODUCTION 



lems of migration and if it encourages him to con- 

 tinue more enthusiastically than ever in the collec- 

 tion of facts and in analysis of the field aspects, it 

 will have achieved its object. It is the writer's 

 belief that not only can biology assist ornithology 

 to elucidate the problems of bird migration, but 

 that ornithology can assist biology in its attempt to 

 discover something more of the true nature of 

 animal behavior. 



The various field aspects of migration are referred 

 to only as necessity arises. Full summaries of what 

 is known today of the subject are to be found in 

 several excellent works, notably Wetmore's very 

 readable little book The Migrations of Birds (Har- 

 vard University Press, 1927. Price $2.50) or 

 Landsborough Thomson's more detailed volume 

 Problems of Bird Migration (Witherby, 1926. 

 Price 18/-). 



